This invention relates to a glow switch starter, and more specifically to an improved glow switch starter with less deviation in starting characteristics, such as starting voltage, initial glow discharge period, etc.
In some glow switch starters used for starting discharge lamps such as preheat-start type fluorescent lamps, metal barium is deposited on the inner wall of a glass bulb as an airtight envelope and on a discharge electrode. The metal barium serves to keep the starting voltage of the glow switch starter at a predetermined value and to reduce the deviation of the value. In a conventional method of depositing metal barium on the glass bulb and electrode, barium azide Ba(N.sub.3).sub.2 is deposited on the inner surface of the glass bulb and the electrode, a stem in which the electrode is set is hermetically sealed in the glass bulb, the glass bulb is evacuated to form a vacuum and is then heated to thermally decompose the barium azide. According to this method, however, the thermal decomposition of the barium azide in the vacuum is performed explosively, so that metal barium from the barium azide deposited on the inner surface of the glass bulb scatters and sticks to the electrode during the thermal decomposition. Consequently, an excessive amount of metal barium is attached to the electrode to lower the starting voltage of the glow switch starter below the desired value. If the amount of barium azide deposited on the inner surface of the glass bulb is reduced to prevent so much metal barium from sticking to the electrode, the desired amount of metal barium may not be able to be deposited on the inner surface of the bulb. As a result, the gettering effect of the metal barium cannot be fully exhibited, so that tht initial glow discharge period of the glow switch starter and hence the ignition time of the lamp will be extended.